gear ratios

Discussion in 'OT Driven' started by Pinan, Feb 15, 2006.

  1. Pinan

    Pinan pagan holidays > * other holidays

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    I tried posting this in the main forum, but got no bites. So Ill try it here.

    quick question about gear ratios. First, I understand teh premise of the mechanical advantage, I am just not sure how to get the physics class to the driveway.

    I am looking at a new car that offers both a 5 speed manual as well as a 5 speed automatic. I have the gear ratios of the two respective trannys.

    5MT 5AT Sport
    3.307 3.620
    1.842 1.925
    1.310 1.285
    0.970 0.933
    0.755 0.692

    My question is this... what is the 'real world' comparison of the two? I understand that for each respective gear, one would be quicker, with lower top end, and the other would be slower, but with a greater top end... what I dont know is which is which. Obviously, I havent driven the car yet... doing my homework first.

    Anyone have any ideas?
     
  2. red97gst

    red97gst New Member

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    unless i'm dyslexic, the MT has shorter gears in 1st and 2nd, and the AT has shorter 3rd, 4th, and 5th gears. So the MT will accelerate better to around 60mph, give or take

    Greater top end isnt something u can base just on the gearing, and Auto trannies have more drivetrain power loss so it will almost never be quicker at ANY speed (save for a straight up drag car) but if they DIDNT, then the auto would accelerate harder in 3rd-5th gears

    Also, having shorter 3rd gear isnt necessarily a good thing for the highway, depending on the power curve of the motor. Sometimes u want longer gears up top, so it stays in the powerband longer

    i havent considered gear ratios in years, so i could be off on this
     
    Last edited: Feb 15, 2006
  3. whathappened2u

    whathappened2u New Member

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    If the gear ratios were the same and the final drive was different it would be much easier to figure out. The AT has a lower geared final drive and a lower first gear so it should be quick from a stop in 1st gear, after that I don't really know what to tell you.
     
  4. Derrict

    Derrict No, I am not Amish OT Supporter

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    If you're able to find and post a dyno graph, it'll show how much hp & torque is available through the RPM range. The gearing is worthless without knowing the engine and it's powerband.
     

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